Many particulate materials arc conveniently transported by truck, although they may also be transported by railcar, barge or by other means. Trucks that are used to transport such materials may include a tractor and an attached trailer having a tank or other container mounted thereon. Such trailers may also be loaded on railcars or barges, or a container may be mounted directly on a railcar or barge. Frequently, these transport containers are referred to as pneumatic containers because of the pneumatic method, involving gas- or air-entrainment, by which they may be loaded and unloaded. Materials that are generally stored or transported in pneumatic containers include agricultural products such as grain, corn kernels, beans, flour, sugar, peanuts and the like, lightweight aggregate products, and intermediate products for various industrial uses such as plastic pellets or powders, coke, lime, silica gel, powdered acid resins, rare earth powders and powdered alumina.
Pneumatic containers generally include one or more product compartments that are usually cylindrical or spherical in shape in order to facilitate unloading by a method which involves pressurizing the compartments. Cylindrical or spherical product compartments are also generally easy to completely empty. Each product compartment is provided with a discharge hopper that may be generally cylindrical or conical in shape. The product compartments are generally enclosed by a sheet metal sheath, especially when the container is mounted on a trailer or other transport device, which sheath provides an aerodynamically efficient outer container surface.
One type of known construction of such pneumatic containers comprises two or more generally cylindrical and horizontally disposed product compartments which are arranged along a common horizontal axis in at least partial fluid communication with each other. A cylindrical or conical discharge hopper is provided for each product compartment, and the axis of each such discharge hopper intersects the product compartment with which it is associated generally at right angles to the axis of the cylinder of the product compartment. Each discharge hopper has a material outlet at the bottom and a valve which controls the entry of material into the outlet. An unloading system is also provided which includes a blower or other mechanism for pressurizing air or another gas. The blower provides the energy required for unloading the material from the container in the form of compressed air or another gas. One end of a pressurizing gas conduit is attached to the blower and the other end to a pressurizing gas inlet in the container. Operation of the blower will compress air or gas and move it through the pressurizing gas inlet into the container, thereby increasing the pressure of the air or gas above the material in the product compartments in the container in order to assist in discharging material through the hopper outlets. One end of a material conveying conduit is also attached to the blower and extends past and connects to each material outlet so that when the product compartment has been pressurized, air or another gas may be directed into the material conveying conduit to entrain material passing through each material outlet and carry it to the discharge end of the conduit. The container may be mounted on a frame which is supported by the chassis of a trailer.
Because the product compartments of the conventional container are in at least partial fluid communication with each other, only one type of product may be transported at a time. Thus it is generally economically necessary that sufficient product of one type be transported to fill the entire container. In addition, because particulate products are not often compatible with each other and facilities for cleaning containers of this type are usually only available at the carrier's terminal, it is generally impossible to transport one product on the forward-haul trip and another on the back-haul.
It would be desirable if a transport container could be developed in which two or more different types of particulate materials could be transported at the same time, or one type of material could be transported on a forward-haul trip and another type of material on the back-haul trip.